1. Field of the Invention
The invention relates to high-pressure discharge lamp provided with a discharge vessel, which vessel is enclosed with intervening space by an outer bulb and fitted with a lamp cap, and provided with an ignition circuit comprising a SIDAC.
2. Description of the Prior Art
A lamp of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 4,520,294. In the known lamp, which is suitable for operation in series with a stabilizer ballast on an AC voltage supply source, the SIDAC is positioned in the outer bulb and provided with a glass envelope as a protection against reduction and evaporation of parts of the SIDAC. Practice has shown, however, that this involves major disadvantages. On the one hand, the manufacture of a SIDAC provided with such an envelope is very difficult, which renders the SIDAC very expensive. On the other hand, the known lamp is found to show a high percentage of early failures owing to blackening of the discharge vessel.
It is attractive, however, to position the ignition circuit including the SIDAC in the outer bulb because of a comparatively simple lamp manufacturing method, one of the reasons being the availability of comparatively much space in contrast to, for example, the lamp cap. In addition, when the ignition circuit is positioned in the outer bulb, only two electric conductors need be guided from the discharge vessel to the lamp cap through this outer bulb. This means a considerable manufacturing advantage compared with constructions in which only a portion of the starting circuit is included in the outer bulb.